Comet Storm is a mythic Instant card from Commander Anthology (CMA), collector number 79. Current market price: $3.66, TCGplayer market prices via Scryfall.
Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.) Choose any target, then choose another target for each time this spell was kicked. Comet Storm deals X damage to each of them.